Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds, found ubiquitously in all environmental compartments. PAHs are considered hazardous pollutants, being of concern to both the environmental and human health. In the aquatic environment, PAHs tend to accumulate in the sediment due to their high hydrophobicity, and thus sediments can be considered their ultimate sink. Concurrently, sediments comprise important habitats for benthic species. This raises concern over the toxic effects of PAHs to benthic communities. Despite PAHs have been the subject of several reviews, their toxicity to freshwater benthic species has not been comprehensively discussed. This review aimed to provide an overview on PAHs distribution in freshwater environments and on their toxicity to benthic fauna species. The distribution of PAHs between sediments and the overlying water column, given by the sediment-water partition coefficient, revealed that PAHs concentrations were 2 to 4 orders of magnitude higher in sediments than in water. The sediment-water partition coefficient was positively correlated to PAHs hydrophobicity. Toxicity of PAHs to benthic fauna was addressed through Species Sensitivity Distributions. The derived hazardous concentration for 5% of the species (HC₅) decreased as follows: NAP (376 μg L^-1) > PHE > PYR > FLT > ANT (0.854 μg L^-1), varying by 3 orders of magnitude. The hazardous concentrations (HC₅) to benthic species were inversely correlated to the hydrophobicity of the individual PAHs. These findings are pertinent for environmental risk assessment of these compounds. This review also identified future challenges regarding the environmental toxicity of PAHs to freshwater benthic communities, namely the need for updating the PAHs priority list and the importance of comprehensively and more realistically assess the toxicity of PAHs in combination with other stressors, both chemical and climate-related.

Zwitterionic compounds (ZIs) have been attracting much attention due to their properties. Unlike ionic liquids – constituted by separated ions – the ZI structures with their cations and anions covalently bonded exhibit added complexity and diversity, suggesting that their ecotoxicological behavior should probably not be extrapolated from those of ionic liquids. This study addresses the aquatic toxicity of ZIs towards the bacterium Allivibrio fischeri and the microalga Raphidocelis subcapitata. Sixteen ZIs comprising five different cationic groups (ammonium, imidazolium, pyridinium, pyrrolidinium and piperidinium) and two anionic groups (sulfonate and carboxylate) were studied, and the relationships between their structure and toxicity are reported. All studied ZIs are harmless or practically harmless for both microalga and bacterium (median effective concentration, EC₅₀ >100 mg L⁻¹), presenting a significantly lower hazardous potential to aquatic species than their ionic liquid counterparts. The results also show that the increased hydrophobicity of ZIs, owing to the increase of the cation alkyl chain or the spacer length, has a significant influence on EC₅₀ values for microalga, which in turn causes higher toxicity. However, no significant differences were observed when considering the various cationic groups of the ZIs studied, unlike what is known for ecotoxicity of the ionic liquids. Also, no relationships were found between the chemical structure of ZIs and EC₅₀ values determined for the bacterium A. fischeri. The structural differences between ZIs and ionic liquids result in different mechanisms of interactions with microalgae and bacteria membranes, which may explain why the ecotoxicity heuristic rules previously reported for ionic liquids do not seem to apply to ZIs.

The efficiency of ozonation depends on the water matrix and the reaction time. Herein, these factors were addressed by assessing the removal of five pharmaceutical and personal care products (PPCPs) by ozonation. The main aims were: (i) to assess the effects of the water matrix on the degradation kinetics of PPCPs, individually and in mixture, following ozonation; and (ii) to assess the ecotoxicological impact of the ozone reaction time on the treatment of a spiked municipal wastewater (MW) added the five PPCPs over several species. The degradation of the PPCPs was faster in ultrapure water, with all PPCPs being removed in 20 min, whereas in the MW, a 30 min ozonation period was required to achieve a removal close to 100%. Increasing the number of PPCPs in the water matrix did not affect the time required for their removal in the MW. Regarding the ecotoxicity assessment, Raphidocelis subcapitata and Daphnia magna were the least sensitive species, whereas Lemna minor was the most sensitive. The temporal variation of the observed effects corroborates the degradation of the added PPCPs and the formation of toxic degradation by-products. The removal of the parent compounds did not guarantee decreased hazardous potential to biological species.